1. Field of the Invention
The present invention relates to an optical deflector that includes a deflector provided with a vibrational system having a movable body with a light deflecting member, and deflects light from a light source by the movable body. Further, the present invention relates to an image forming apparatus using the optical deflector.
2. Description of the Related Art
As a conventional optical deflector, a galvano-mirror as illustrated in FIG. 8 has been proposed. See also JP 07-175005 A. This galvano-mirror is driven with an electromagnetic force. In the galvano-mirror, a mirror 56 is provided on a movable plate 53, and the movable plate 53 is supported by a silicon substrate 50 through torsion springs 54. The movable plate 53 can be tilted about an axis defined by the torsion springs 54 in a reciprocating manner. A driver for driving the movable plate 53 is comprised of a flat coil 55 and permanent magnets 60 to 63. The optical deflector is accordingly of an electromagnetic type in which a current is caused to flow through the flat coil 55, and the Lorentz force for driving the movable plate 53 is generated due to the current flowing through the flat coil 55 and the magnetic flux generated by the magnets 60 to 63. In FIG. 8, reference numeral 51 designates an upper-side glass substrate, reference numeral 52 designates a lower-side glass substrate, and reference numeral 57 designates an electrode terminal.
As another conventional optical deflector, an actuator of the same electromagnetic type including a movable body with a reflective mirror has been proposed. See, e.g., JP 2001-305471 A. This electromagnetic actuator has been devised for overcoming the following disadvantageous phenomena. In general, the resonance frequency of an electromagnetic actuator is liable to drift due to a change in temperature, or with time. Accordingly, where a modulating current at a preset resonance frequency continues to be supplied to the flat coil, the maximum tilt angle of the movable body cannot be stably maintained for the reasons described above. In this conventional optical deflector, therefore, the electromagnetic actuator is designed to achieve an appropriate reciprocating rotation of the movable body at the resonance frequency, or an appropriate regulation of the maximum tilt angle of the movable body, without using an additional detecting portion. Further, proposed in this conventional optical deflector is a signal generator for generating a resonance frequency signal corresponding to the resonance frequency of the electromagnetic actuator.
To achieve these objects, the coil in the conventional optical deflector is used for the detector as well as for the driver for driving the movable body. For the detection, voltage or current induced in the coil is employed. Information of the time at which the actuator passes a certain tilt or deflection angle is detected based on the voltage or current induced in the coil serving as the detector.
However, where the optical deflector as disclosed in JP 2001-305471 A is used for deflecting a light beam modulated according to an image signal, there is a possibility that the temperature of the optical deflector varies depending on contents of the image signal. Thus, the motion of the light deflection fluctuates, and the quality of the image formed is likely to decrease. To improve the quality of the image, therefore, it would be helpful to correct the motion of the light deflection in accordance with a modulation rate of the image signal.